Many human activities affect groundwater quality in Wyoming. Plate 27 shows sites where groundwater could be impacted by trona mills (yellow triangle), uranium mills (red square), petroleum refineries (orange diamond), and underground injection (blue circle). Other human activities which comprise potential sources of groundwater pollution are: leaking underground storage tanks (Chapter 26); irrigated agriculture (Chapter 14) and weed/pest control; municipal, commercial, and industrial landfills; domestic sewage ponds; commercial and industrial wastewater ponds; powerplants; commercial oil and gas wastewater disposal ponds; and subsurface and surface mining of coal. Naturally occurring groundwater contamination is discussed in Chapter 29.

Mill tailings from the processing of trona have high salinity levels. The typical total dissolved solids levels from mill tailings ponds range from 45,000 to 50,000 milligrams per liter. Trona mining is concentrated in western Sweetwater County. The salinity of groundwater is increasing near the tailings ponds at several trona mines. In some cases, plumes of salinity have migrated three miles from the source.

Uranium mining can also impact groundwater quality by releasing radionuclides and other toxic pollutants. Uranium mining areas are concentrated in northern Converse, northeastern Carbon, eastern Fremont, and western Natrona counties. In 1978, Congress passed the Uranium Mill Tailings Radiation Control Act, providing for reclaimation of mill tailings processing sites. Two of these sites are in Wyoming: one is located two miles southwest of Riverton; the second, 30 miles north of Glenrock.

Groundwater pollution has been identified beneath petroleum refineries in Casper, Cheyenne, Cody, Evansville, Glenrock, Newcastle, and Sinclair. Petroleum distillates may contain a number of cancer causing compounds, posing a significant health risk if the contaminated water is used as drinking water.

No hazardous wastes are injected into underground wells in Wyoming, but the process is used to dispose of waste from industrial and municipal sources (8 wells), petroleum related activities (about 4,000 wells), in-situ uranium operations (350 wells), and underground coal-gasification (400 wells).

Irrigated crop production and weed/pest control have impacted groundwater in the state. Nitrates and/or pesticides have been discovered in the groundwater around the Kendrick and Riverton irrigation projects and in the vicinity of Powell, Worland, Torrington, and the Bridger Valley. Pesticides have also affected groundwater in Crook and Weston counties. Since irrigated agriculture is concentrated adjacent to rivers with a dependable water supply, alluvial aquifers are particularly subject to impact. Alluvial aquifers with consistently elevated levels of pesticides are found under the following streams: Bitter Creek (near Powell), Crow Creek (near Cheyenne), and the Greybull, Bighorn, Shoshone River, Belle Fourche, Clear Creek, and the Popo Agie rivers.

Plate 27 was digitized from Hogan (1988).